Return to Mars question

I don't think this is the book I'm looking for but when I was say 14, I read an old book from the library that really influenced me. It's possible I'm conflating two books I read at the same time, but it's about a group of scientists who travel to a few nearby star systems in the hope of finding a planet to colonise, but each has its drawbacks. One planet has an atmosphere rich in laughing gas and foolishly they almost succumb.

Eventually, they return to the Solar System and decide Mars is the best planet after all. But, they discover remains of an ancient civilization. What's more, spirits of these departed beings floated and danced about around them in a cave (a phrase like, "Myriads of" dancing lights or something was used).

What's more, these aliens had once lived on a fifth planet before destroying it and colonising Mars. I think they were evil...

Would anybody know what book I'm talking about?